The main causative agents of cat-scratch disease are Bartonella henselae, tiny, gram-negative bacilli. The disease usually has a benign course with the development of a papule at the inoculation site, followed by regional lymphadenopathy. In most cases, complete resolution occurs, but in immunocompromised hosts, the course of the disease can be aggravated. A patient received methotrexate and corticosteroids for 3 months due to rheumatoid arthritis. He developed fever, exanthema and leukopenia under methotrexate therapy. Dark red indurations with central ulcerations at his right thigh revealed a further problem apart from the methotrexate-induced leucopenia and immunosuppression. The ulcerations were the remainders of recurrent scratches from the patient's cat. The patient's antibody titers against Bartonella henselae remained low and inguinal lymph node swelling was only for a short time to be observed, this reaction obviously weakened as a result of the immunosuppression. However, the typical course, the exclusion of other reasons for the exanthema and the rapid improvement of the patient's condition after antibiotic treatment ascertained the diagnosis. In immunocompromised hosts, diseases with a typically benign course can become severe and life-threatening illnesses. Ownership of pets should be taken into consideration before onset of an immunosuppressive therapy.